This application claims the benefit of Korean Application No. 200147535, filed Aug. 7, 2001 in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to microwave ovens, and more particularly, to a microwave oven with a humidity detector that has a simple construction and is inexpensively fabricated.
2. Description of the Prior Art
In general, microwave ovens are apparatuses that cook food using microwaves. In a conventional microwave oven, the intensity of microwaves and the cooking time are determined according to a state of food to be cooked. The material, shape and the kind of the food placed in the cooking chamber of the microwave oven determines the absorption of the microwaves and the amount of energy required. As such, the microwave oven detects and assesses the state of the food being cooked using a variety of sensors. Based upon the assessed state, the microwave oven and care out a cooking operation.
As shown in FIG. 9, a conventional microwave oven comprises a body 1, the interior of which is partitioned into a cooking cavity 2 and a machine room 3. A door 4 is hinged to the body 1 so as to close the cooking cavity 2. The microwave oven also has a control panel 5, which is installed at the front wall of the body 1 and is provided with a variety of control buttons. A humidity sensor 6 is installed in the body 1 to sense the operational conditions of the food in the cooking cavity 2.
The cooking cavity 2 has an opening in front, and has a turntable cooking tray 2a rotatably mounted on a bottom of the cooking cavity 2. An air inlet 7a is formed at a front portion of a sidewall 7 of the cooking cavity 2 so as to allow the cooking cavity 2 to communicate with the machine room 3. Air flows from the machine room 3 into the cooking cavity 2 through the air inlet 7a. An air outlet 8a is formed at a rear portion of the opposite sidewall 8 of the cooking cavity 2 so as to discharge the air from the cooking cavity 2 to the atmosphere exterior to the microwave oven.
A magnetron 3a, a cooling fan 3b, an air guide duct 3c, and other similar devices (not shown) are installed within the machine room 3. The magnetron 3a generates the high-frequency electromagnetic waves, while the cooling fan 3b sucks atmospheric air into the machine room 3 to cool the elements 3a, 3b installed within the machine room 3. The air guide duct 3c guides the air inside the machine room 3 to the air inlet 7a and into the coking cavity 2. The cooling fan 3b is installed between the magnetron 3a and a rear wall of the machine room 3. In order to allow the atmospheric air to flow into the machine room 3, a predetermined area of the rear wall of the machine room 3 is perforated to form a plurality of air suction holes 3d. 
The humidity sensor 6 is installed on a sidewall 8 of the cooking cavity 2 at a position adjacent to an air outlet 8a. Thus, the humidity sensor 6 is located. In an air discharging passage leading from the cooking cavity 2. The humidity sensor 6 thus senses the humidity of the exhaust air discharged from the cooking cavity 2 through the air outlet 8a and that is defined by a surface of the humidity sensor 6. The humidity sensor 6 is connected to a circuit board (not shown) installed in the control panel 5, and outputs a signal to the circuit board.
When turning on the microwave oven containing food on the cooking tray 2a, the high frequency electromagnetic waves are radiated from the magnetron 3a into the cooking cavity 2 and the food is cooked using the generated electromagnetic waves.
During such an operation of the microwave oven the cooling fan 3b is rotated to form a suction force to suck the atmospheric air into the machine room 3 through the air suction holes 3d as to cool the elements installed in the room 3. The air is, thereafter guided to the air inlet 7a by the air guide duct 3c and introduced into the cooking cavity 2 through the air inlet 7a. The air inside the cooking cavity 2 is exhausted along with vapor (moisture) generated from the food, which is exhausted in the form of humidity to the atmosphere through the air outlet 8a as shown by the arrows of FIG. 9. Therefore, it is possible to remove odor and vapor generated from food during the operation of the oven. When the exhaust air from the cooking cavity 2 to the atmosphere, it comes into contact with and is turned by the humidity sensor 6. The humidity sensor 6 senses the humidity of the exhaust air, and outputs a signal to the circuit board of the control panel 5. The circuit board of the control panel 5 controls the operation of the magnetron 3a, the cooking tray 2a and the cooling fan 3b in response to the signal from the humidity sensor 6, thus automatically cooks the food on the tray 2a. 
The conventional microwave oven shown in FIG. 9 uses the humidity sensor 6 to detect the cooking state of the food. The conventional microwave oven detects the moisture formed from the food in the form of humidity, and controls the cooking operation according to the detected moisture.
The conventional humidity sensor 6 is a porous humidity sensor made of a semiconductor ceramic of MgCrO4xe2x80x94TiO2. The conventional semiconductor ceramic humidity sensor 6 has a characteristic in that its value of resistance is varied according to the amount of moisture that infiltrates into the pores/holes of the semiconductor ceramic humidity sensor 6.
However, the conventional semiconductor ceramic humidity sensor 6 is disadvantageous in that its fabrication cost is high. In addition, when remainders exist in the holes, the detection performance deteriorates and the overall life span of the sensor 6 is shortened.
Accordingly, to solve the above and other problems, an object of the present invention is to provide a microwave oven with a humidity detector that has a simple construction and is inexpensively fabricated.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
In order to accomplish the above and other objects, a microwave oven according to an embodiment of the invention includes a magnetron to generate microwaves, a cooking chamber to contain food to be cooked using the generated microwaves, a humidity detector to detect humidity formed as the food is being cooked, the humidity detector being provided at an outlet of the cooking chamber to receive air containing moisture from the cooking chamber and including first and second electrodes formed on a board and spaced apart from each other at a predetermined interval to form a gap therebetween into which the air is received, and a control unit to control the cooking operation of the microwave oven according to an output of the humidity detector.